1. Field of the Invention
The present invention relates generally to perpendicular magnetic recording media, methods of manufacturing the same, and magnetic storage units including the same, and more particularly to a perpendicular magnetic recording medium having a magnetic layer in which magnetic particles are separated by a non-magnetic material, a method of manufacturing the same, and a magnetic storage unit including the same.
2. Description of the Related Art
Magnetic storage units are employed in large-scale systems to a variety of apparatuses such as computers and communication devices of personal use. In each use, magnetic storage units are required to record information with higher density and transfer information at higher speed.
According to perpendicular magnetic recording, information is recorded in a magnetic recording medium by magnetizing the recording layer of the magnetic recording medium in a direction perpendicular to its substrate surface. Accordingly, compared with longitudinal (in-plane) magnetic recording, the recorded information is less likely to disappear. Therefore, perpendicular magnetic recording can perform recording with higher density than longitudinal magnetic recording.
Perpendicular magnetic recording media are formed by stacking a soft magnetic underlayer formed of a soft magnetic material on a substrate and stacking a recording layer on the soft magnetic underlayer. Usually, the recording layer is formed of a CoCr-based alloy. The CoCr-based alloy is formed by sputtering while applying heat to the substrate, so that non-magnetic Cr is segregated at the grain boundary between Co-rich magnetic particles of the CoCr-based alloy, thereby magnetically isolating the magnetic particles from one another.
On the other hand, the soft magnetic underlayer forms the magnetic path of magnetic flux flowing into a magnetic head at the time of reproduction. In a crystalline soft magnetic material, spike noise is generated because of magnetic domains. Therefore, the soft magnetic underlayer is formed of an amorphous or microcrystalline body, for which it is difficult to form magnetic domains. Accordingly, the heating temperature at the time of forming the recording layer is restricted in order to avoid crystallization of the soft magnetic underlayer.
Therefore, a recording layer having a so-called granular columnar structure where magnetic particles of a CoCr-based alloy are separated from one another by a SiO2 non-magnetic parent phase is proposed as a recording layer that isolates magnetic particles from one another and does not require heat treatment at high temperature. Further, it is also proposed to form a Ru film as the underlayer of a recording layer in order to form a columnar structure in which the c-axis of a magnetic particle grows in a direction perpendicular to the surface of a substrate and cause the magnetic particles to grow at substantially equal intervals (see, for example, Japanese Laid-Open Patent Application No. 2005-353256).
The magnetic particles of the recording layer perform crystal growth on the surface of the Ru film. Accordingly, the crystal orientation of the magnetic particles is significantly affected by the crystal orientation of the Ru film. That is, the (0002) crystal planes of the Ru film preferentially serve a's growth planes, and the Co (0002) crystal planes of the magnetic particles grow on the growth planes. An increase in the proportion of the (0002) crystal planes of the Ru film which planes are not parallel to the substrate surface affects the orientation of the Co (0002) crystal planes. This increases the proportion of those of the multiple magnetic particles whose magnetocrystalline easy axes (c-axes) are not perpendicular to the substrate surface, thus degrading so-called magnetocrystalline easy axis orientation dispersion. In particular, the Ru film is formed in an inert gas atmosphere of Ar gas or the like by sputtering, and the crystal orientation of the Ru film in its initial growth condition is easily disturbed in a manufacturing apparatus because of the effect of oxygen gas adsorbed on the inner wall of a film formation chamber. This disturbance has an adverse effect on the entire Ru film and further on the magnetic particles of the recording layer. This degrades recording and reproduction characteristics, thus causing the problem of making it difficult to achieve a further increase in recording density, that is, so-called higher recording density.